Conductivity
Conductors, Semiconductors, Superconductors, and Insulators
In this lab we will consider the structures and properties of some special solids known as conductors, semiconductors and superconductors. Text readings on these topics can be found in Chapter 12 of the Silberberg textbook. Your instructor will also give you information on these subjects. Some web links to relevant information can be found at
Semiconductors are the basis of so much of our modern electronic technology because the electric current flowing through them can be controlled with modest amounts of energy. This is due to the presence of a gap between the valence (nonconducting) band and the conduction (conducting) band. The larger this band gap is, the more energy is required to make the material conduct electricity.
Conductors, most being metals, have a very small band gap, that is, the outer valence electrons exist in sublevels with unfilled orbitals. This means that a very small energy boost via heat, light, or electricity can promote a valence electron to another orbital or level. This leaves a vacancy or "hole" where the electron was before, into which another electron can move. The movement of electrons therefore is accompanied with a movement of holes and an electric current is passed.
In this lab you will measure the resistance of a good conductor, the band gap of several different semiconductors LEDs and the special behavior of ceramics known as superconductors. You will also explore many of the factors which influence the size of the band gap, including temperature and LED composition.
Part 1: Testing the resistance of a conductor
Part 2: Testing the band gap in semiconductors (LEDs)
Part 3: Measuring the Effects of Temperature on LEDs (band gaps)
experimental procedures
